Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.62   10.582%   $65.929   $65.93   $65.95   $65.90  
  Purchase #2 $65.67   8.239%   $71.0806   $71.08   $71.10   $71.10  
  Purchase #3 $97.98   3.291%   $101.2045   $101.20   $101.20   $101.20  
  Purchase #4 $76.44   11.828%   $85.4813   $85.48   $85.50   $85.50  
  Purchase #5 $230.72   11.499%   $257.2505   $257.25   $257.25   $257.30  
  Purchase #6 $178.65   4.215%   $186.1801   $186.18   $186.20   $186.20  
  Purchase #7 $13.44   9.224%   $14.6797   $14.68   $14.70   $14.70  
  7 purchase totals = $722.52       $781.8057   $781.80   $781.90   $781.90